Refraction

What is refraction? What is the normal? What is the critical angle?

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Refraction is the bending of light.

The normal is a line perpendicular to surface. If θincidence = 90° there is no refraction

The critical angle is the smallest angle of incidence at which total internal reflection occurs.

 

Refraction occurs because of different speeds of light in different mediums.

 

Light bends towards the normal as it travels from a fast medium to a slow medium.

Light bends away from the normal as it travels from a slow medium to a fast medium.

 

 

The frequency of light does not change during refraction. What changes?

Since frequency is a constant. The velocity and wavelength therefore must change. v = f λ

 

 

Refraction explained using Fermat's Principle

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Refraction and Mirages

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Refractive index

The refractive index of a substance, n, is the ability to bend light. Those substances with a higher refractive index will bend light more when compared using the same angle of incidence.

Substance Refractive Index
Air 1.00
Water 1.33
Vitreous Humor (eye ball jelly) 1.33
Glycerin 1.473
Pyrex 1.474
Virgin olive oil 1.47
Sunflower oil 1.47
Paraffin oil 1.475
Microscope immersion oil 1.52

 

Glycerol and pyrex glass have a similar index of n=1.47

How do they behave together?

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Snell's Law Song, n1 sinθ1 = n2 sinθ2

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Snell's law song - lyrics

 

Snell's Law Explained

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v = c/ n where v= velcocity of light in a medium and c=speed of light in a vacuum and n=refractive index of medium

 

 

Total Internal Reflection.

Did you know that the critical angle is the angle at which the incident ray travelling into a denser medium is bend 90° away from the normal?

The critical angle(θc) can be detemined by Snell's law setting the angle of refraction to 90°

 

ni sinθc = nr sin90

 

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